Critical Role of Zur and SmtB in Zinc Homeostasis of Mycobacterium smegmatis
Critical Role of Zur and SmtB in Zinc Homeostasis of Mycobacterium smegmatis
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DOI：
10.1128/msystems.00880-19
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发表时间：
2020-03-01
期刊：
影响因子：
6.4
通讯作者：
Goethe, Ralph
中科院分区：
文献类型：
--
作者：
Goethe, Elke;Laarmann, Kristin;Goethe, Ralph
锌稳态对于细菌细胞至关重要，因为不平衡会影响生存能力。然而，在分枝杆菌中，对锌代谢的了解并不完整。耻垢分枝杆菌 (MSMEG) 是一种环境、非致病性分枝杆菌，被广泛用作研究分枝杆菌代谢和致病性的模式生物。 MSMEG 如何维持锌稳态尚不清楚。 SmtB 和 Zur 是细菌锌代谢的重要调节因子。在分枝杆菌中，这些调节因子由操纵子编码，而在其他细菌物种中，SmtB 和 Zur 在不同的基因座上编码。在这里，我们表明 smtB-zur 操纵子始终存在于分枝杆菌属中，但仅在诺卡氏菌属、糖丝菌属和白喉棒状杆菌中发现。通过RNA深度测序，我们确定了MSMEG的Zur和SmtB调节子，并将它们与锌饥饿或过量后的转录反应进行比较。我们发现了一个特殊的基因组聚类，其表达受到 zur 缺失和锌饥饿的强烈诱导。这些基因编码锌输入蛋白，如 ZnuABC 和另外三种假定的锌转运蛋白，包括孔蛋白 MspD，以及替代核糖体蛋白。相比之下，只有少数基因受到 smtB 缺失和锌过量的影响。锌出口商 ZitA 主要受 SmtB 监管。此外，结合启动子和染色质免疫沉淀测定的转录分析揭示了 smtB-zur 操纵子本身的特殊调节：smtB-zur 的明显不依赖于锌的组成型表达是由 SmtB 和 Zur 敏感的共调节引起的。总的来说，我们的数据揭示了分枝杆菌锌稳态的未知特性。 重要性 锌对于许多生物过程至关重要，因为它是酶的重要辅助因子以及调节蛋白和 DNA 结合蛋白的结构成分。因此，所有活细胞都需要锌来维持恒定的细胞内水平。然而，过量的锌是有毒的。因此，需要严格控制细胞锌稳态。在细菌中，这是通过转录调节因子来实现的，转录调节因子的活性是通过锌依赖性构象变化来介导的，从而促进或阻止它们与 DNA 的结合。 SmtB 和 Zur 是分枝杆菌中重要的拮抗作用细菌调节剂。它们感知飞摩尔范围内锌浓度的变化，并调节锌获取、储存和输出的基因转录。在这里，我们分析了 SmtB 和 Zur 在耻垢分枝杆菌锌稳态中的作用。我们的结果揭示了对分枝杆菌中锌稳态转录过程及其调节的新见解。
Zinc homeostasis is crucial for bacterial cells, since imbalances affect viability. However, in mycobacteria, knowledge of zinc metabolism is incomplete. Mycobacterium smegmatis (MSMEG) is an environmental, nonpathogenic Mycobacterium that is widely used as a model organism to study mycobacterial metabolism and pathogenicity. How MSMEG maintains zinc homeostasis is largely unknown. SmtB and Zur are important regulators of bacterial zinc metabolism. In mycobacteria, these regulators are encoded by an operon, whereas in other bacterial species, SmtB and Zur are encoded on separate loci. Here, we show that the smtB-zur operon is consistently present within the genus Mycobacterium but otherwise found only in Nocardia, Saccharothrix, and Corynebacterium diphtheriae. By RNA deep sequencing, we determined the Zur and SmtB regulons of MSMEG and compared them with transcriptional responses after zinc starvation or excess. We found an exceptional genomic clustering of genes whose expression was strongly induced by zur deletion and zinc starvation. These genes encoded zinc importers such as ZnuABC and three additional putative zinc transporters, including the porin MspD, as well as alternative ribosomal proteins. In contrast, only a few genes were affected by deletion of smtB and zinc excess. The zinc exporter ZitA was most prominently regulated by SmtB. Moreover, transcriptional analyses in combination with promoter and chromatin immunoprecipitation assays revealed a special regulation of the smtB-zur operon itself: an apparently zinc-independent, constitutive expression of smtB-zur resulted from sensitive coregulation by both SmtB and Zur. Overall, our data revealed yet unknown peculiarities of mycobacterial zinc homeostasis.IMPORTANCE Zinc is crucial for many biological processes, as it is an essential cofactor of enzymes and a structural component of regulatory and DNA binding proteins. Hence, all living cells require zinc to maintain constant intracellular levels. However, in excess, zinc is toxic. Therefore, cellular zinc homeostasis needs to be tightly controlled. In bacteria, this is achieved by transcriptional regulators whose activity is mediated via zinc-dependent conformational changes promoting or preventing their binding to DNA. SmtB and Zur are important antagonistically acting bacterial regulators in mycobacteria. They sense changes in zinc concentrations in the femtomolar range and regulate transcription of genes for zinc acquisition, storage, and export. Here, we analyzed the role of SmtB and Zur in zinc homeostasis in Mycobacterium smegmatis. Our results revealed novel insights into the transcriptional processes of zinc homeostasis in mycobacteria and their regulation.